Telephone system



T. F. CROCKER TELEPHONE SYSTEM Filed Jan. 18, 1943 oct. 3,y 1944.

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TELEPHONE SYSTEM Filed Jan. 18, -1945 12 sheets-sheet 2 swITcH MECH, 22o 22| c.L.R.

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l INVENTOR. THOMAS F. OROOKER BYM,M.MM

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` TELEPHONE SYSTEM Filed Jan. 18, 1945 Y 12 Sheets-Sheet 10 -CIO25 Fl/GO l04l I MARGINAL INVENTOR. THOMAS F.YGROCKER BY la? MM Oct. 3, 1944.

T. F. cRocKER TELEPHONE SYSTEM Filed Jan. 18., 1943 12 Sheets-Sheet 11 mail' LINK IDENTITY SEDER APPARATUS `ATTOR NEYS Oct. 3, 1944. I T. F. cRocKER l2,359,626

TELEPHONE SYSTEM Filed Jan. 1s, 1945 12 sheets-sheet 12 C50|==a y :H4:

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uNlTs malo INVENTORT THOMAS F. cRocKeR ATTORNEYS Patented 'Oct. 3, 1944 TELEPHONE SYSTEM Thomas F. Crocker, Chicago, Ill., assigner to Automatic Electric Laboratories, Inc., a corporation of Delaware Application January 18, 1943, Serial No. 172,712

20 Claims.

The present invention relates to telephone systems and more particularly to such systems comprising a central oice provided with switching links and a iir'st operator switchboard, a remote "control center provided with a second operator switchboard, and an arrangement whereby the switching links ma;7 be selectively controlled from the various operator positions at either one of the two switchboards to set up connections.

It is an object of the present invention to provide in a telephone system of the type noted an improved arrangement for identifying, in conjunction with a controlling operator position at either one of the two switchboards, 'the particular one of the switchingr links controlled therefrom.

Another object of the invention is to provide in a telephone system, including a group of switching links selectively controllable from an associated operator position, improved link idenvtity apparatus manually controllable from the operator position. 4

A further object-of the invention is to provide in a telephone system, including a group of switching links which are selectively operable to set up connections, an improved arrangement responsive to the release of a connection for releasing the switching link utilized and for automatically identifying the switching link at an associated operator position.

A further object of the invention is to provide in a telephone system, including a group of lswitching links and an operator switchboard, an improved arrangement for distributing calling ones of the switching links to idle ones of theI operator positions at the switchboard or to an associated call storage unit when all of the operator positions are busy.

Further features of the invention pertain to the particular arrangement oi the circuit elements of the system, whereby the above-outlined and additional operating features are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specication taken in connection with the accompanying drawings, in which Figure 1 illustrates the general arrangement of a telephone system embodying the present invention; Figs. 2 to l2, inclusive, taken together, illustrate the details of a system having incorporated therein the features of the invention as briey outlined above; and Fig, 13 illustrates the mode of combining Figs. 2 to 1,2, inclusive, to form a unied system.

Description of the apparatus incorporated in the system Referring now more particularly to Fig. 1 of the drawings, the telephone system there illustrated comprises a central ofce 20, a distant exchange 30 and a remote control center 40. The central oflice -20 and the distant exchange 30 are interconnected by a group of toll lines, including the toll line 202; and the central lofce 20 and the remote control vcenter 40 are interconnected by a number of transfer trunks, in-

cluding the transfer trunk |00|. The central oice 20 serves a number of local telephone stations, including the telephone station T, and comprises a toll switchboard 600 provided with a number of operator positions, the rst operator position 05| being illustrated. Similarly, the remote control center 40 comprises a toll switchboard S00 provided with a number of operator positions, the rst operator position 90| being illustrated. More particularly, the toll switchboard B00 and the toll switchboard 900 comprise a corresponding number of paired operatorpositions interconnected by the transfer trunks mentioned. lFor example, the first operator position at the toll switchboard 600 corresponds to and is paired with the first operator position at the toll switchboard 900, for a purpose more fully explained hereinafter; and the operator positions mentioned are interconnected by the transfer trunk |00|.

The distant 'exchange 30 comprises a toll operator position 20| of any suitable type terminating the ends of the toll lines 202 etc. in the group in the distant exchange 30; while the ends of the toll lines 202 etc. in the group are terminated in a groupv of toll line circuits in the central oiiice 20, the toll line circuits being of any suitable type. Specically, the toll line 202 is terminated in the central oflce 20 in a toll line circuit 203. In the central office 20 a telephone line 209 extends to the telephone station T and is provided with a line circuit 2|0 individual thereto of any suitable type. Also thecentral oiiice y2l) comprises a local switch train, including a number of under-selector links 2|5 etc. of any suitable type; idle ones of the nder-selector links are istributed for use by an associated allotter 2|3 of any suitable type. Also the central oiiice 20 comprises a number of C. L. R. trunk circuits 2|'| etc. of any suitable type. The iinder-selector link 2|5 has access to the telephone line 209 eX- Atending t'o the line circuit 2|0 and to an rincomcircuit 2|1. v

Further the central oice 20 comprises a toll switch train including a group of 100 toll links 300 etc.; the toll link 300 comprising a link finder 200, a toll selectorV 400 and an access switch 3|0.

Also a toll link distributor 201 of any suitable typel is provided in the central ofce 20 for distributing idle ones of the toll links 300 in a predetermined order, for a purpose more fully explained herein-V after. Also the toll switch train includes a nurnber of toll connectors 4 0 etc. of any suitable type. The link nder 20,0 has access to an outgoing trunk 204 extending from the'toll line circuit 203 and to an outgoing trunk 2 I'8 extending from the C. L, R. trunk circuit 211; the toll selector 400 has access to an incoming trunk 205 extending to the toll line circuit 203 and to an incoming trunk 405 extending to the toll connector 4|0; While the access switch 3|0 has access to each of a number of control trunks 602 etc. and alsoto a call storage unit 100'provided in the central oice 20. Finally the toll connector 4|0 has access to the telephone line 209 extending to the line circuit 2|0. Further the central ofce 20 comprises a number of linkV identity display apparatus 500 etc. and a number of link identity sender apparatus |000 etc. individually associated with the operator positions 60| etc. at the toll switchboard 600; also the link identity sender apparatus |000 etc. are individually associatedY with corresponding ones of the transfer trunks etc. Similarly, the Vremote control center 40 Vcomprises a number of Y link identity display apparatus 800 individually associated with the operator positions 90| etc. I

at the toll switchboard 000. Also the link identity display apparatus 800etc. are individually associated with corresponding onesfof the transfer Ytrunks |00| etc.

Accordinglydt will be understood that the access switches 3|0 etc. of the various toll links 300 etc. have access to the various control trunks 602 etc., as well as to the call storage unit 100 as previously noted; Each control trunk 602 etc.

Vis selectively connectible to the corresponding operator position 60| etc. at the toll switchboard 600 or to the' corresponding transfer trunk extending between the centralofiice and the remote control center 40. Thus the control trunk 602 is either connected to the rst operator position 60|l at the toll switchboard 600 or to the corresponding transfer trunk |00| extending be-` tween the central oflice 20 and the remote control center 40. The transfer trunks |00| etc. are individually connected to the corresponding operator positions 90| etc. at the toll switchboard 900 in the remote control center 40.

Preferably, each ofthe toll links is identical to the toll linkr300 which comprises` as shown in Figs. 2 to 4, inclusive, a link nder 200, a toll selector 400 and an access switch 3|0. as previously noted. The link finder 200 is of the 200-point type and comprises a switch mechanism 220 of the Strowger type, including a first wiper set provided with three wipers 22| to 223, inclusive,V a second wiper set provided with three wipers 2214 to 226, inclusive, and a vertical control wiperV 221. Each of the wiper sets is Vprovided. with a semi-cylindrical contact bank including ten vertically spaced-apart levels of contact Sets arranged in circumferentially spaced-apart relation; while the vertical control wiper 221 is provided with a contact bank including ten vertically spaced-apart control contacts. Each. Qi the ing trunk 'als extending to the c. L. R. trunk wiper sets is mounted for both vertical and rotary movements while the vertical control wiper` 221 is mounted for only vertical movement. Also the switch mechanism 220 comprises a vertical magnet M228 lfor driving the wiper sets step by step in the vertical direction away from their normal vertical positions, a rotary magnet M230 Yfor driving the wiper sets step by step in the rotary direction away from their normal rotary positions, and a release magnet M232 for releasing the wiper sets and for causing them to be returned to' their normal rotary and vertical positions. Also associated with the switch mechanism 220 are two sets ofswitch springs S233and S236 o which are actuated by the movement of the wiper sets in the vertical direction away from their nor- L mal vertical position. Further the link finder 200 comprises a relay group, switch-through relays R240 and R250, a start relay R260, a hold relay R330, a cutoff relay R335, a cut-through relay R340, a control relay R350, a transfer relay R360, a link identity relay R365, a stop relay R310, a cutoff relay R315 and a connect relay R380; and a control network connected and arranged in a manner more fully described hereinafter.

The toll selector 400 is of the Strowger` type and is connected and arranged in a substantially conventional manner; While the access switch 3|0 is of the rotary type, including six wipers 3|| to 3|6, inclusive, provided with individually associated contact banks, and a magnet M3|1 for driving the wipers noted step by step in the clockwise direction. g

The call storage unit 100, shown in Fig. 7, comprises a relay group, including a busy relay R1 |0 and six storage relays R120, R130, R140, R150.

R and R110, six storage lamps L18| etc., a'

busy lamp L181; and a control network connected and arranged in a manner more fully described hereinafter.

Preferably, each of the operator Vpositions at the toll switchboard 6,00 is identical to the rst operator position 60| which comprises, as shown in Fig. 6, an operator telephone 68| lof any` suitable type, a relay group including a transfer relay R620, a cut-off relay R630','a call relay R550 andV an answer relay R650, and a register sender 680 of any suitable type. Also the firstoperator posi- Y tion 60| comprises a linelamp L616; a send pilot lamp L611; and a key set including a transfer key K660, a display release key K66 a split,` key X662, an error key K663, a link identity key K664, a talk key K665, a hold key K666, a busy key K661, a coin rear key R668, a coin front key K669 and a ring key K610; and a control network connected and arranged in a manner more fully described hereinafter.

Preferably, each 0f the link identity display apparatus individually associated with the operator positions at the toll switchboard 600 is identical to the link identity display apparatus 500V individually associated with the first operator position 60 The link identity display apparatus 500 comprises, as shown in Fig. 5, a relay group including ten tens relays R530, R535 and R540 etc.; ten slave relays R550, R555, R560 etc.`indi display apparatus 500 comprises ten tens lamps,

including two l lthe #l tens lamp being illustrated, and ten units "start relay R920, a first digit stop relay R930, ra

laimps, the #1, #2 and #0 units lamps being illustrated; and a control network connected and -arranged ina manner more fully explained hereinafter.

At this point it is noted that the central office 20- comprises one hundred toll links which are 4consecutively numbered from to 00; and that the particular toll link which is utilized in setting up a connection from-the rst operator position 60| at the toll switchboard 600 may be identied by the link identity display apparatus 500 .through the operation Aof the corresponding tens and units relays therein, -causing the illumina- -tion of the corresponding tens and units lamps .arranged before the associated position 60|. y

Preferably, each of the link identity sender apparatus individually associated with the operator pos-itions at the toll switchboard 600 and with the transfer `trunks is identical to the link identity sender apparatus |000 Aindividually associated withy the rst operator position 60| and with the transfer trunk |I. The link identity rsender apparatus |000 comprises, as shown in Figs. to l2, inclusive, a relay group, including three pulse relays R|0|0, R|020 and R|030, two stop relays R|040 and R|000, a restart yrelay R|050, afcontrol relay R|010, a release relay R|080, a transfer relay RI I0, ten counting relays RI |20, Rl |30, RI |00, RIISD, Rl |60 etc., ten tens relays R|260, Rl2-1ll, R|280 etc., tenslave relays R'I-240, Rl245, R|250 etc., and ten units relays R|2|0,'R|220, R|230 etc.; and a control network connected and arranged in a manner more fully explained hereinafter. For example, the counting relays R! |20, Rl |30, RI |40, RI |50 and RI |60 may comprise the respective first, second, third, ninth and tenth counting relays; the tens relays R|260, R|210 and R|280 may comprise the respective first, second and tenth tens relays; while rst operator the units relays R|2|0, R'I220 and R|230 may comprise the respective rst, second and tenth `units relays.

At thi's point it is noted that the particular toll link which is utilized in setting up a connection from the first operator position 90| at the toll switchboard 900 may be identified by the link identity sender apparatus |000 through the operation of the corresponding tens and units relays therein, causing the link identity sender apparatus |000 to transmit the corresponding tens and'units digits over the transfer trunk |00I.

Preferably, each operator position at the toll switchboard 900 is identical to the rst operator position 90| which operator position is identical to the corresponding rst operator position 60| at the toll switchboard 600. lMore particularly, the first operator position 90| comprises, as illustrated in Fig, 9, positionequipment etc. which is identical to that provided at the first operator position 60|; which position equipment includes the display release key K902, the transfer key K903, the error key K900- and the link identity keyv K905 illustrated.

Preferably, each of the link identity display apparatus individually associated with the operator positions at the toll switchboard 900 is identical to the link identity display apparatus 800 individually associated with the -first operator position 90|. The link identity display apparatus 800 comprises, as shown in Figs. 8 and 9, a relay group including a pulse relay R820, a transfer relay R830, ten counting relays R840, R850, R860,

R810, R880 etc., a digit relay R9|0, a rst digit 76 second fdigit start relay R940, a second digit stop relay R950 and ten tens relays R960, R910, etc. For'exampla the tens relays R960 and R910 may comprise the respective first and tenth tens relays; while the counting relays R840, R850, R860, R810 and R880 lmay comprise the respective first,-second, third, fourth and tenth counting relays. Also the link identity display :apparatus 800 comprises tentens lamps, the #land #0 tens lamps being illustrated, and ten units lamps, the #1, #2, #3, #4 and #0 units ylamps being illustrated; and a control network connected and arranged in a manner more fully explained hereinafter.

At this point it is noted that the particular toll link which is utilized in setting up a connection from the first operator positionl at the toll switchboard 900 may be identified by the link identity display apparatus 800 through the operation of the corresponding tens and countingrelays therein, causing the illumination of the corresponding tens and units lamps arranged before the associated first operator position 90|.

A better understanding of the connection and arrangement of the apparatus incorporated in Initial operation of a toll Zink First assuming that a toll call is initiated at the telephone station T in the central office 20, the subscriber first removes the receiver of'the telephone instrument thereat from its associated switchhook, thereby to cause the -line circuit `2|0 terminating the telephone line 209 to operate and control the allotter 2|3 over the start conductor C2|2. The allotter 2|3 is controlled to assign an idle one of the lnder-selector links in the local switch train, such, lfor example, as the finder-selector link 2| 5. controls the'nder-selector link 2|5 over the cable 2|4 in order to cause the finder-selector link 2|5 to seize the telephone line 209 extending to the yline circuit 2| 0 and to return dial tone thereover. The subscriber at the calling telephone station T then dials a digit thereat over the telephone line 209 t'o the finder-selector link 2| 5, whereupon the finder-selector link 2 I5 oper-A ates rst to select thegroup of trunks and then an idle trunk therein extending to the group of C. L. R. trunk circuits. For example, assume that the finder-selector link 2|5 seizes the trunk 2| 6 extending to the C. L. R. trunk circuit 2|1. At this time, the C. L. R. trunk circuit 2|1 is controlled in order to cau'se ground potential to be applied to the common start conductor C206 extending to the toll link distributor 201.

The application of ground potential to the common start conductor C206 causes the toll link distributor 201 to initiate operation of the previousli7 selectedidle toll link in the associated group, such, for example, as the toll link 300 illustrated. More particularly, the toll link distributor 201 has selected the cable 210 extending to the idle toll link 300 and applies ground potential to the finder start conductor C211 thereyin in order to complete an obvious circuit for The allotter 2|3 then v Vpie path, including the Contacts 231 of the set of way of the vertical magnet M228 to the vertical conductor C215 in the cable 210. The application of battery potential in the link nder 200 to the vertical conductor C216 in the cable 210 causes the toll link distributor 201 to apply ground potential thereto in order to complete an obvious Y circuit for energizing the vertical magnet M220.

When thus energized the vertical magnet M228 operates in order to drive the wiper` sets of the switch mechanism 220 one step in the vertical direction away from their normal vertical position and to complete, at the contacts 229, an

obvious path for applying ground potential to the ,interrupter conductor C215 in the cable 210. When the wiper sets of the switch mechanism 220 are driven one step in the vertical direction vaway from their normal vertical positions the Vsets of switch springs S233 and S236 are actuated, for a purpose more fully explained herein- Vafter, and the vertical control wiper 221. en-

gages the rst contact in the associated contact bank.

The application of ground potential to the interrupter conductor C215 in the cable 210 causes the toll link distributor 201 to interrupt the application of ground potential to the vertical conductor C216, thereby to interrupt the previously traced circuit for energizing the vertical magnet M228, whereby the latter magnet restores in order ,to'interrupt, at the contacts 229, Vthepreviously mentioned path Vfor applying ground potential to the interrupter conductor C215 in the cable 210. At this time the vertical controlrwiper 221 engages the first contact in the associated contact bank, whereby ground potential is applied to the test conductor C213 in the cable 210 in the event the trunk 2l8 extending from the C. L. R. trunk circuit 2|1 is terminated by a contact'set in theY rst level of the contact bank associated with the rst'wiper set of the switch mechanism 220.

vOn the other hand, in the event the trunk 2l8 is not terminated by a contact set in the first level of the contact bank associated with the'rst wiper set of the switch mechanism 220, no ground potential appears upon the rst contact engaged by the vertical control wiper 221 and, accordingly, ground potential is not applied to the test conductor C213 in the cable 210. In the lastmentioned event, when ground potentialV is removed from the interrupter conductor C215 in the Vcable 210, the toll link distributor 201 again operates in order to apply ground potential to the vertical conductor C216 in the cable 210, whereby the vertical magnet M228 is reoperated in order to drive the wiper sets of the switch mechanism 220 an additional step in the vertical directi-on. Accordingly, the wiper sets of the switch mechanism 220 are driven step by step in the vertical direction by the vertical magnet M228 until Ythe rst wiper set is driven to the level of contact sets in the Yassociated contact bank upon g which theV trunk 2l8 extending to the calling C. L. R. trunk circuit 2|1-is terminated; whereupon ground potential is applied by way of the vertical control Vwiper 221 to the test conductor C213 in the cable 210.

The application of ground potential to the test conductor C213 in the cable 210 causes the toll link distributor 201 to be controlled, whereby ground potential is removed from the vertical conductor C216 in the cable 210 and is applied to the rotary conductor C212 in the cable 210, The application of ground potential to the rotary conductor C212 in the cable 210 completes an obvious circuit, including the contacts 262, 256

and 246, for energizing the rotary magnet M230, v

whereby the latter magnet operates in` order to drive the wiper sets of the switch mechanism 220 one step in the rotary direction away from their normal rotary position and to complete, at the contacts 23|, an obvious alternative path for applying ground potential to theinterrupter conductor C215 in the cable 210. The applicationV of ground potential to theY interrupter conductor C215 in the cable 210 causes the toll link 4distributor 201 to be controlled, whereby ground potential is removed from the rotary conductor C212 in the cable 210 inA order to interrupt the previously traced circuit for energizing the rotary m-agnet M230. The rotary magnet M230 then restores, thereby to interrupt, at the con--Y tacts 23|, the previously mentioned path for applying ground potential to the interrupter conductor C215 in the cable 210. At this timethe 'control Wiper 223 of the rst wiper set of the switch mechanism 220 tests the rst contact set in the previously selected levelV in order to determine whether the trunk 2l8 extending to the calling C. L. R. trunk circuit 2|1 is terminated thereby. In the event the trunk 2l8 is not terminated by the rst contact set in the level. mentioned, further operation of the toll link dis--v tributor 201 takes place, whereby ground potential is reapplied to the rotary conductor VC212 in order to effect reoperation of the rotary magnetV M230. Accordingly, the wiper sets of the switch mechanism 220 are driven step by step in the rotary direction by the rotary magnet M230 until the control wiper 223 of the rst wiper set tests the contact set terminating the trunk 2|0 extending from the calling C'. L. R. trunk circuit 2|1; at which time battery potential in the calling C. L. R. trunk circuit 2|1 is applied by way of the control conductor of the trunk 2l8 to the test wiper 223. Also, at this time, ground potential is applied to the vertical control wiper 221, whereby an obvious circuit, including the contacts 254, is completed for energizing the 'lower winding of the switchthrough relay R240 in order to cause the latter relay to operate. Upon operating, the switch-through relay R240 interrupts, at the contacts 246, a further point in the previously traced circuit for energizing the rotary magnet M230, and completes, at the contacts 245, a holding circuit, including the contacts 26|, for energizing the upperwinding of the switch-through relay R240 in series with the rotary magnet M230. When this series circuit is completed the switch-through relay R240 is retained in its operated position; however, the rotary magnet M230 does not operate due to the high series resistance of the upper winding of the switch-through relay R240.

Also the switch-through relay R240 completes, at the contacts 243, an obvious connection between Vthe winding ofthe hold relay R330 and the control wiper 223 of the first wiper set of the switch mechanism 220,y whereby the winding Vof the hold relay R330 is energized in multiple with the lower winding of the switch-through relay R240 and in series with the equipment in the C. L. R. trunk circuit 2|1, whereby the hold relay R330 operates and Ythe equipment in the C.

of the iirst wiper set of the switch mechanismr 220 and the line conductors C40| and C402 extending to the toll selector 400, and interrupts, at the contacts 244, a point ina test circuit traced hereinafter for energizing theupper winding of the switch-through relay R250, thereby" positively to prevent operation ofthe latter re-` lay at this time. Further the switch-through relay R240 completes, at the contacts 248, a circuit, including the contacts 359, 312, 381 and3l8,

for energizing the magnet M3|1 of ytheaccess'Y switch 3I0, thereby to initiate operation of the latter switch for a purpose morefullyf explained hereinafter. Finally the switch-through relay R240 completes, at the contacts 241, an obvious connection,l including the contacts 256, 262 andY 263between the rotary conductor C212 andthe guard Vconductor C214 in the cable 210; `When the rotary conductor C212 and the guard con ductor C214 are thus connected together the toll link distributor 201 is releasedwherebythe previously traced circuit for energizing the winding of the start relay-R260 is interrupted in order to cause the latter relay to restore shortly there'- after, the start relay R260 being of the slow-to release type. R260 interrupts, at the contacts 26|, a' point in the previously traced holding circuit for energize ing the upper winding of the switch-through relay'R240 in series with the rotary magnet M230. However, arialternative holding circuit substantially identical to that previously tracedhas been' completed at this time, at the` contacts 33|, incident to the operation of the hold relay R330. Accordingly, the switch-through relay R240- remains in its operated position at this time. In'- cident to the operation of the equipment in the C. L. R. trunk circuit-,2H to its seized position, battery potential therein is removed from; the

Vertical control wiper 221, thereby to interrupt the previously traced original operating circuit for energizing the lower winding of the switchthrough relay R240; hoWever the latter relay.

remains in itsloperated position due to. the. cornpletion` of` the previously traced holding circuit for. energizingthe upper winding thereof in series with the rotary magnet-M230.` Also, upon restoring, the start relay R260 completes, at the contacts 264, an obvious path, including the con- Upon restoring, the start relay change 30, the toll operator first selects an idle one of the toll lines, such, for example, as the toll line 202, then connects the position equipment thereto, andv then operates the associated position equipment in order to cause ringing current to be projected over the toll line 202 to the terminating toll line circuit 203. circuit 203 then operates in order to cause ground potential to be applied Vto the common start contacts 2350i the set of switch springs S233, for

applyingground potential to the guard conductor C214 inthe cable 210, therebyk positively to pre- 201` from selecting vent the toll link distributor the busy. toll link 300 at this time. it is` noted that, when the tolllink dered busy. as explained abo-ve, ground potential therein is removed from the all-trunks-busyconductor C211. Accordingly, when all ofthe one hundred toll links are busy, ground potential is completely removedv from the all-trunks-busy conductor C211 in the cable 210, whereby the toll link distributor 201 is rendered completely busy.

Accordingly, at this time, the link finder 200 of the toll link 300 has operated to find the tru'rlk 2|8.ext`ending from the calling C. L. R. trunk circuit 2|1 and operation of the access switch 3|0 is initiated, for a purpose more fully explained hereinafter.

Now lassuming that a toll call is initiated at the toll'operator position 20| in the distant ex- In passing,

300 is renductor C206, whereby operation of the tolllink distribtuor 201 is initiated in order to initiate operation of the previously selected tollv link. Again assuming that the toll link distributor 201 has preselected theidle toll 4link 300 illustrated, operation of the link iinder 200 is initiated in the manner previously explained, More particularly, the operation of the link finder 200 under the control of the tollV link distributor 201 isY the same as that previously described except that in this case it is assumed that the trunk 204 extending from the toll line circuit 203 is terminated in the contact bank associated with the` second Wiper set of the switch mechanism 220. Accordingly, in thiscase, whenthe second wiper set of the switch mechanism 220 engages the contact set in the associated contact bank terminating the trunk 204, battery potential is applied to the control wiper 226 thereof, thereby to complete an obvious circuit, including the contacts 244, for energizing the upper winding of the switch-through relay R250. When thus. energized the switch-through relay R250' operates to interrupt, at the contacts 256, a further point in the previously traced circuit for energizing the' rotary magnet M230, and completes, at the contacts 255, a holdingcircuit, including the contacts 26| and 246, for energizing the lower winding, thereof in series with the rotary magnet M230.` Also the switch-through relay R250 completes, at the contacts 258, an alternative circuit, including the contacts 249, 359, 312, 381 and SIB', for energizing the magnet M3|1 of the access switch 3|0`. Further the switch-through relay R250 completes, at the contacts 25| and 252, an obvious connection, including the contacts 336, 33T, 316' and 311, betweenthe line wipers 224' and 225 of the second wiper set and the line conductors C401 and C402 extending to the toll sclector 400. The otherl functions performed inci dent to the `operation of the switch-through relay R250 are identicaltothose performedincident to the operation ofthe switch-through relay R240, as previously explained.

Accordingly, at this time, the link finder 200 o-f'the'toll link 300 has operated to find the trunkv 2704 v extending from the calling toll line circuit 203 and operation of the accessswitchf 3|0 is initiated, for a. purpose more fully explained hereinafter.

Considering nowk the operation of the access switch 3`|0, it is noted-that this switch operates tofseize an idle one of the control trunks- 602y etc. or to seize the call storage unit 1.00 in the ks 602 etc. are busy As previously noted, the iirst `control trunk 602 is either connected to the=1rst operator position 60| at the toll switchboard 600, in the eventthe transfer relay. R620. occupies its event all of. the controltrun restored position, or.. isV connected. tocthe first in the event the transferr transfer trunk" |001-, relay R620'occupies its operatedfposition;.while the first' transfer trunk |001 is connected tothe rst'operator 'position-00| at the'toll switchboard 900? Accordingly-in the event' the nist cont-roiv trunk 602" is connected to the rst operator po- The toll line marked as idle vor as Ybusy,'depending upon the respective idle or busy condition of the first operator position 60|, event the first control trunk 602 is connected to the iirst transfer trunk |00|, it is either marked asv idle or as busy, depending upon Vthe respective idle or busy condition ofthe rst operator position 90| at the toll switchboard 900. Specically, the rst control trunk 602 is respectively marked as idle or as busy by the applicationrof battery potential or ground potential,

respectively, tothe `control conductor C326 thereof. More particularly, either battery potential or groundrpotential in the rst operator position 60| at the toll switchboard 600 is applied to the conductor-C651, depending upon the respective idlek orY busy condition thereof and may be connected by wayrof the contacts 620 to the control conductor VC326 of the first control trunk 602. Similarly, either battery potential or ground pof tential in the nrst operator position 90| at the toll switchb-oard 900 is applied to theY conductor C6|6 of the rst transfer trunk |00I, depending upon the respective idle or busy condition thereof, and maybe connected by way of the contacts 629 to the control conductor C326 Vof the rst control-trunk 602, Accordingly, it will be understood that, when one of the control trunks 602 etc. is idle, the access switch 3|0 operates to seize the idle control trunk; on the other hand, when all Yof the control trunks 602 etc. are busy,

the access switch 3|0 operates to seize the call storage unit 100.

Y Y Answering a. call at the toll switchboard in the central o cev It is contemplated that'the toll switchboard 600 in the central office 20 will be utilized normally' and that the toll switchboard 900 in the remote control center 40 will be utilized under emergency conditions. Accordingly, under normal operating conditions, the various control trunks 602 etc.

will be connected to the corresponding operatorV positions at the toll switchboard 600. Hence, the transfer relay R620 will normally occupy its restored position, whereby the control trunk 602 is directly connected to the first operator position 460| at the toll switchboard 600.

Assuming that the first operator position 60| at the toll switchboard 600 is idle at this time, battery potential isapplied by way of the #1 contacts of the busy key K661, the winding of the Vcall relay R640 and the contacts 654 to the con- Yat the contacts 3|8, the-previously traced circuit for energizing the magnet'MSH. The magnet M3|1 then restores, thereby 'to drive the wipers noted of Vthe access switch 3|0 one step in the clockwise direction and to recomplete, at the contacts 318, the previously traced cir-cuit for energizing the magnet M3|1. Accordingly, the magnet M3|1 operatesintermittently, thereby to drive On the other hand, in theV quently the rst operator position 60| at the toll Y Considering the Y Y 2,359,626 'sition tel at the toll switchboard 600,11; is either the wipers noted of the access switch 3|0 step by step in the clockwise direction until an idle control trunk is tested. Assuming that the rst control trunk 602 is the first idle control trunk tested by the access switch 3|0, when the control wiper 3|6 thereof engages the contactV in the associated contact bank terminating the control conductor C326 of the first control trunk 602, a circuit, including the conductorV C396 and the contacts 386, 358 and 333, is completed for energizing the Winding of the .stop relay R310 in view y of the fact that battery potential appears upon the control conductor C326 of the first control trunk 602. When thus energized the stop relay R310 operates to interrupt, at the contacts 312, a further point in the previously traced circuit for energizing the magnet M3|1, thereby positively to arrest further operation of the access switch 3|0, whereby the latter switch has selected the nrst control trunk 602 and conseswitchboard 600 at this time. It is noted that, during the operation of the access switch3l0, ask

the control wiper 3|6 thereof engages contacts in the associated contact banks'terminating the control Yconductors of busy control trunks, ground potential is encountered thereby, completing an obvious path, including the conductors C396 and the contacts 386, 358 and 333, for short-circuit- Y ing the winding of the stoprelay R310.

The above-traced circuit for energizing the Winding of the stop relay R310-includes in series the winding of the call relay R640 at the rstV operator position 60| at the toll switchboard 600,

whereby the latter relay is operated. Upon'operating, the call relay R640 completes, at the contacts 642, aholding circuit, including the contacts 652, 654 and the #l contacts of the busy key K661, for energizing the Winding thereof, and

an obvious circuit L616, thereby to completes, at the contacts 643, for illuminating the line lamp indicate to the operator at the rst operator position 60| that a call has been extended thereto and is waiting to be answered. Also they call relay R640 completes, at the contacts 64|, an obvious path, including the contacts 622', for applying ground potential tothe chain conductor C619, thereby to prepare a point in a chain cir- Y' cuit for energizing the Winding of the busy relay R1|0 in the call storage unit V100. At this point itis noted that the above-mentioned circuit for energizing the winding of the busy relay R1|0 is completed when all of the control trunks V602 etc.

are connected to busy operator positions at the toll switchboards 600 and '900, whereby the latter relay operates for a purpose more fully explained hereinafter. Further Ythe call relay R640 completes, at the contacts 642, an obvious path, including the contacts 652 and 620, for applying ground potential to the control conductor C326 of the rst control trunk 602, thereby to mark the latter trunk as busy'to the access switches of the other toll links having `access thereto.

Also, upon operatingthe stop relay R310 in the link finder 200 completes, at the contacts 31|, an Yobvious circuit for energizing the winding of the connect relay R380, thereby to cause the latter relay to operate. Upon operating, the connect relay R380 completes, at, the contacts 385, a holding circuit, including the conductor C396, `the control wiper 3|6 of thelaccess switch 3|0 and the engaged contact in the associated contact bank and the grounded control lcon- 'Y nect relay R380 interrupts, at the contacts 386, the previously traced circuit for energizing the winding of the stop relay R310, thereby to cause the latter relay to restore. Also the connect relay R380 interrupts, at the contacts 381., a further point in the previously traced circuit for energizing the magnet M3|1, prepares, at the contacts 384, a circuit traced hereinafter for energizing the winding of the cutoff relay R315, andprepares, at the contacts 383, a circuit traced hereinafter for energizing in series the windings of the cut-through relay R340 and the .cutoff relay R335. Further the connect relay R380 completes, at the contacts 33| and 382, a connection between. the line wipers of the selected wiper set of the switch mechanism 220 and the line conductors C32| and C322 of the first control trunk 602; the last-mentioned connection including the contacts 24|, 242 or 25|, 252 and the contacts 336, 331, 316, 311, 38| and 382, the conductors C39| and C392 and the Wipers 3| and 3|2 of the access switch 3| 0 and the engaged contacts in the associated contact banks.

When the operator at the first operator position. 60| observes the illuminated line lamp L616, she answers the call byoperating the talk key K665, whereby there is completed, at the #l and #2 contacts thereof, an obvious connection between the operator telephone 68| and the line V,conductors C32| and C322 of the first control trunk 602; the last-mentioned connection including the contacts 632, 634, 622 and 624; whereby the operator telephone 68| at the first operator position 60| is operatively connected by way of the previously traced circuit to the selected Wiper set of the link iinder 200 and consequently to the calling circuit. The calling party advises the operator at the first operator position 60| concerning the extension of the call at this time. Also when the talk key K665 is operated there is completed, at the #4 con.- tacts thereof, an obvious circuit for energizing thewinding of the answer relay R650, thereby to cause thelatter relay to operate and interrupt, at the contacts 652 and 654, the previously traced holding circuit for energizing the winding of1 the call relay R646, whereby the latter relay restores. Also the answer relay R650 completes, at the contacts 653, an alternative path, including the #3 contacts .of the talk key K665, the conductor C651 and the contacts 620, for applying groundpotential to the control-conductor C326 of the first control trunk 602. Further the answer relay R650 completes, at the contacts 65| a point in multiple with the contacts 64|, for applying ground potential by way of the contacts 622 to the chain conductor C619 .for vthe purpose previously noted. Moreover, the answer relay R650- completes, at the contacts 655, an obvious path for applying ground potential to the conductor C618 extending to the register sender 680, whereby the register sender 680 is renderedY operative to register one or more digits in response to operation of the associated key set. Finally the answer relay R650 completes, at` the-contacts 656, an obvious circuit for illuminating the send pilot lamp L611, thereby to indicate tothe operator at the first operator position. 60| that the register sender 600 has been seizedv and is in readiness to receive one or more digits. Upon restoring, the call relay R640, interrupts, at the contacts 643, the previously mentioned circuit for illuminating the line lamp L616 indicating that the call has been' answered at the rst operator position60|-.

After the operator at the first operator position 60| has learned the destination of the call she operates the key set associated with the register sender 680 in order to cause one or more digits to be registered therein. When a digit is registered in the register sender 680 ground potential is returned over the conductor C615, thereby to complete an obvious circuit for energi'zing the winding of the cutol relay R630. When thus energized they cutoiT relay R630 operatesshortly thereafter, as the latter relay is of the slow-to-operate type, to interrupt, at the contacts 632 and 634, the previously traced connection between the operator tele-phone 68| and the line conductors 032| and C322 of the first control trunkv 602. Also the cutoi relay R630 completes, at the contacts 63| and 633, obvious connections respectively including the contacts 622 and 624 between the line conductorsC`32l and C322 of the first control trunk 602 and the conductors C614 and C613 extending to the register sender 680; completes, at the contacts 635, an obvious connection, including the contacts 626, between the conductor C323 of the first control trunk 602 and the conductor C612 extending to the register sender 680; and completes, at the contacts 636, a connection, including the contacts 626 and the error key R663, between the conductor C324 of the rst control trunk 602 andthe conductor C61! extending to the register sender 680. At this time high resistance ground potential in the register sender 630 is applied to the conductor 061|, thereby to complete a cir-V cuit, including the contacts 636, the error key X663, the contacts 628, the conductor C324 of the first control trunk 602, t-he Wiper 3I4 of the access switch 3l0 and the engaged contact in the associated contact bank, the conductor C394 and the contacts 383, for energizing in series the windings of the cut-through relay R340 and' the cutoff relay R335 in the link finder 200. When this series circuit is completed the cutoff relay R335 operates; however, the cut-through relay R346 does not operate as the latter relay is of the marginal type. Upon operating, the cutofi relay R335 interrupts, at the contacts 336 and 331, the previously traced connection between the selected wiper set of the link finder 260 and the line conductors C40| and lC402 extending to the toll selector 400, and completes, at the contacts 338, an obvious path for applying ground potential to the control conductor C403 extending to the toll selector 460. The application of ground potential to the control conductor C403 rende-rs the toll selector 400 operative in response to a digit transmitted thereto. Also, at this time, a loop circuit is completed between the register sender 660 and the toll select r`400,l

this loop circuit including the line conductors C46| and C402', the contacts 316,Y 311, 38| andv 382, the conductors 039| and C362, the line wipers 3|| and 3|2 of the access switch 3|0 and-v the engaged contacts in the associated contact banks, the line conductors 032| and C322 of the first control trunk 602, the contacts 622, 624,

63| and 633, and the conductors C514 and C613 extending to the register sender 680:.

The register sender 636 operatesat this tiniein order to interrupt the above-traced loop circuit in accordance with the rst digit registered therein, whereby a corresponding number of impulses constituting a digit are transmitted tothe toll selector 406 in order to cause corresponding operation thereof. The toll selector 400 responds to thei'irst digit toselect acorresponding group 7 extending to the of trunks and then operates automatically to select an idle trunk in the selected group, all in accordance with conventional practice. More particularly, the toll selector 400 may be operated to select a trunk extending to an idle toll line circuit, such, for example, as the toll line 205 toll line circuit 203 terminating Vthe toll line 202 extending to the toll Voperator-position in the distant exchange 30. On the other hand, the toll selector 400 may be operated to select a trunk extending to an idle toll connector, such, for example, as the trunk 405 extending to the tolll connector 4l0. In the last-mentioned case, further Yoperation of the register sender 630 wouldproceed, whereby the toll connector 4|3 is selectively operative to se- Y lect a telephone line accessible thereto,such, for example, as the telephone'lineV 209, extending to the line circuit 2|0 and to the telephone station Tall in accordance with Vconventional practice.

YAfter all of the digits registered in the register sender 680 have been sent therefrom, direct ground potential is applied to the conductor C61|, thereby to complete a low resistance circuit identical to that previously traced for energizing in series thewindings of the cut-through relay R340 and the cutoff relay R335, whereby Ythe cutoff relay R335 is retained in its operated position and the cut-through relay R340 operates.

The cut-through relay R340 operates at this time asfit is of the marginal type, as previously noted. Upon operating, thel cut-through relay R340 completes, at the contacts 342, an obvious circuit, including the contacts 35,4, for energizing the upper winding of the control'relay R350, and

an obvious multiple circuit, including the contacts 354 and 351 and the resistor 343, for energizing the lower Vwinding of the control relay R350. When both the upper and lower windings of the control relay R350 are thus energized the latter relay operates partially, thereby to interrupt, at the contacts 351, the previously traced circuitY for energizing theY lower winding thereof and to complete, at the contacts 356, an obvious path, including the contacts 248 or 258 andthe contacts i! and 342, for short-circuiting the lower winding thereof, whereby further operation of the control relay R350 is positively prevented at this time. Also the cutfthrough relay R340 completes, Yat the contacts 34|, an obvious path for applying batterypotential by way of VC61| the previously traced circuitV for energizing in series'the windings of the cutoff relay R335 Y and the cut-through relay R340 is interrupted,

thereby to cause-these relays to restore. Upon restoring, the cut-through relay R340 interrupts,

at the contacts342, the previously traced path for short-circuiting the lower winding of the control relay R350, whereby an obvious circuit, in-

cluding the contacts 248 or 258 and the contacts 356, is completedY for energizing in series the x upper and lower windings of the control relay R350. When thus energizedv the latter relay operates fully to complete, at the contacts 35|, an obvious alternative path for applying ground potential to the control conductor C403 extending to the toll selector 400. Also the control relay R350 interrupts, at the contacts 352, a further point in the previously traced path for applying resistance battery potential to the control conductor C404 extending to the toll selectorY 400,

and completes, at the contacts 353, an obvious connection between the winding of the hold relay R330 and the control'conductor C404. Further the control relay R350 prepares, at the conwiper set of the link finder 200 and the line con- Y f ductors C40| and C402 extending to the toll selec- Vthe resistor334 and the contacts 352 to the conV tor 400. Y

When ground potential is removed'from the conductor C615 the previously traced circuit for energizing the winding of the cutoff relay R630 is interrupted, l'thereby to cause the latter relay to restore and interrupt, at the contacts 63|, v633, 635 and 636, the previously traced connections between the conductors of the first control trunk 602 and the conductors extending to the register sender 680. Also theV cutoff relay R630 recompletes, at the contacts 632 and 634, the previously traced connection between the operator telephoneV 68| and the link nder 600.

Inorder to ring the called party the operator at the first operator position 60| operatesthe ringV key K610-to its front position, thereby to com- Vplete, at the #8 contacts thereof, an obvious alternative circuit forenergizing the winding of the cutoi relay R630 in order to cause the latter relay to reoperate shortly thereafter. Also when the ring key K610 is operated there is prepared, at

, the #3 contacts thereof, an obvious path forapplying resistance ground potential to the conductor C61I, thereby to complete the previously traced circuit for energizing in series the windings of the cut-through Vrelay `R340 and the cutoffV relay R335V when the cutoff relay rR630 operates, whereby the cutoff relay R335 operates and the cut-through relay R340 remains in its restoredV position, the cut-through relay R340 being of the marginal type, as previously noted. Upon operating, the cutoff relay R335 interrupts, atY the Ycontacts 336 and 331, the previously mentionedV connection between the' selected wiper set of the link nder 200 and the line conductors of the toll selector 400. Finally, at the #7 and #4 contacts ofthe ring key K610, obvious paths are prepared for respectively connecting ground and resistance battery potentials to the respective line conductors C32| and C322 of the rst control trunk 602 and consequently to the respective line conductors C40| and C402 extending to the toll selectorY 400, which paths are completed when the cutoil relay R630 operates. Finally, ,upon operating the cutoff relay R630 again interrupts, at the con-l tacts 632 and 634, the previously traced rconnec- -tion to the operator telephone 68| and completes the vconnections traced above. The application of ground and resistance battery potentials, respectively, to the line conductors C40| and C402 ex-V tending to the toll selector 400 causes operation thereof, whereby ringing current is projected overY the trunk seized thereby and consequently 'over the called circuit. Y 

